In September 2022 my main alternator (PP 60 amp) failed after 472 hours in service. I was in Prescott, AZ at the time. I flew back on the backup alternator (B+C 40 amp) without any issues.
Back at home I removed and disassembled the PP alternator. It was clear that some of the diodes were blown. My plan was to replace the diodes and use the alternator again. To my surprise I also found that the rear outer bearing shell was loose in its housing and could rotate inside the housing. The bearing itself was smooth as can be and spun normally. This did not seem normal to me. I wrote to Hartzell to report what I believed was a new (to me) mode of failure and an unacceptable mode of failure. I have always set the belt tension per Vans instructions using the torque-slip method and did not think that the belt tension was excessive to explain the loose rear bearing. At this time I was already planning on replacing the PP alternator with another make.
Within a couple of hours, I received a detailed response from Hartzell. I copy the response from Timothy Gauntt from Hartzell below with his permission. I was impressed with their rapid response as well as the improvements that were made to the later model alternators. I now still have a PP alternator and will see what the future holds!
"Thank you for your feedback. Regarding our AL12-EI60 kits and/or the 99-1012 alternator in those kits, there have been production improvements implemented since we purchased the product line from the legacy Plane Power company. In short, what many owners have experienced is a known and resolved issue to us. We feel there was a design discrepancy in the product prior to our acquisition. To explain; originally, there are four bolts that secured the front and rear housings. Two of these bolts have “feet” incorporated that secure the stator assembly. If the stator is not secured, it will loosen, contact the rotor and “spin”, ultimately failing the alternator rectifier assembly and/or rear bearing. The housings clamp together with no gap between them as found in other typical alternator designs so stator retention was dependent on the housing tolerances and through bolt torque, especially on the through bolts with the “feet”. We upgraded this design several years ago which now requires the stator be a press fit into the rear housing and that, along with the original “feet”, correctly positions and secures the stator assembly. This has fully rectified the known field issue. Failures of this type would have been the most prevalent in the 2018 and prior manufacturing dates by serial number. (H-Sxxxx = 2018, H-Rxxxx = 2017, H-Qxxxx = 2016, etc.) The serial number provided indicates the alternator was manufactured in approximately the 38th week or 2013.
We also believe a Plane Power customer should expect to get more than 470 hours’ time-in-service from any of our products. To that end, please complete the linked form and return per the form instructions so we can replace the alternator to you as a customer service. https://planepower.aero/aircraft-alternator-support/warranty/"
Back at home I removed and disassembled the PP alternator. It was clear that some of the diodes were blown. My plan was to replace the diodes and use the alternator again. To my surprise I also found that the rear outer bearing shell was loose in its housing and could rotate inside the housing. The bearing itself was smooth as can be and spun normally. This did not seem normal to me. I wrote to Hartzell to report what I believed was a new (to me) mode of failure and an unacceptable mode of failure. I have always set the belt tension per Vans instructions using the torque-slip method and did not think that the belt tension was excessive to explain the loose rear bearing. At this time I was already planning on replacing the PP alternator with another make.
Within a couple of hours, I received a detailed response from Hartzell. I copy the response from Timothy Gauntt from Hartzell below with his permission. I was impressed with their rapid response as well as the improvements that were made to the later model alternators. I now still have a PP alternator and will see what the future holds!
"Thank you for your feedback. Regarding our AL12-EI60 kits and/or the 99-1012 alternator in those kits, there have been production improvements implemented since we purchased the product line from the legacy Plane Power company. In short, what many owners have experienced is a known and resolved issue to us. We feel there was a design discrepancy in the product prior to our acquisition. To explain; originally, there are four bolts that secured the front and rear housings. Two of these bolts have “feet” incorporated that secure the stator assembly. If the stator is not secured, it will loosen, contact the rotor and “spin”, ultimately failing the alternator rectifier assembly and/or rear bearing. The housings clamp together with no gap between them as found in other typical alternator designs so stator retention was dependent on the housing tolerances and through bolt torque, especially on the through bolts with the “feet”. We upgraded this design several years ago which now requires the stator be a press fit into the rear housing and that, along with the original “feet”, correctly positions and secures the stator assembly. This has fully rectified the known field issue. Failures of this type would have been the most prevalent in the 2018 and prior manufacturing dates by serial number. (H-Sxxxx = 2018, H-Rxxxx = 2017, H-Qxxxx = 2016, etc.) The serial number provided indicates the alternator was manufactured in approximately the 38th week or 2013.
We also believe a Plane Power customer should expect to get more than 470 hours’ time-in-service from any of our products. To that end, please complete the linked form and return per the form instructions so we can replace the alternator to you as a customer service. https://planepower.aero/aircraft-alternator-support/warranty/"